Water contaminated with salts over 1,000 parts per million (ppm) is not fit for human consumption. In many parts of the World, the major sources of water are brackish and must be processed before they are fit for human consumption. Not only are these salty waters found in coastal areas where the major water source is seawater, but also in landlocked areas where the only available water lies deep under the surface of the Earth. Much deep-well water is full of dissolved solids, including a number of salts. The problem of brackish water in landlocked areas has many problems. Not only is it expensive to remove salt from the brackish water, there is also the problem of waste disposal from whatever system is implemented. Another facet to the problem is the ability to modify a solution to fit various sized communities depending on their fresh water needs. There is a limited amount of naturally occurring fresh water.
There are many procedures known in the art for separating ions and other dissolved solids from water but most of them require large amounts of energy and extensive knowledge to operate. Examples include distillation, reverse osmosis, ion exchange and electrodialysis. While these aspects may not be significant impediments for large-scale water supply systems, they can impose severe burdens when it comes to operating such systems for small-scale and field applications.
Capacitive deionization is another means of separating ions from an ionic fluid. This method typically encompasses two electrodes with spaced-apart end plates, one at each end of the cell, separated with an insulator layer that is interposed between each end plate and an adjacent end electrode. Each end electrode includes a single sheet of conductive material having a high specific surface area and sorption capacity, such as a carbon aerogel composite. As the ionic fluid enters the cell, it flows through a channel defined by the electrodes, substantially parallel to the surfaces of the electrodes. By polarizing the cell, ions are removed from the ionic fluid and are held in the electric double layers formed at the carbon aerogel surfaces of the electrodes. Once the cell is saturated with the removed ions, the cell is regenerated by discharging the electrodes and releasing the ions held at the electrodes. In the typical setup, the output pipe is closed with a valve prior to regeneration and the flow is redirected to an alternate waste pipe. When the electrodes are discharged, the ions are released from the electrodes and flow out through the waste pipe. Once a sufficient amount of ions are leased, the system is deemed to be regenerated. At that point, the operator can recommence the deionization process by closing the valve to the waste pipe, recharging the electrodes, and reopening the valve to the output pipe.
Through the use of microscale technology, capacitive deionization can be applied to solve both the energy problem and the large-scale system issue simultaneously. Electric fields are effective at pulling charged particles through a medium over short distances, and microtechnology allows for these small distances to be used in conjunction with electric fields to efficiently remove ions from water and produce a clean flow that can be collected for subsequent use. Since an electric field is produced by a voltage gradient, it is possible to create high voltage potentials without requiring large currents, which results in a very low power usage.